Pl. -i. [L., erroneous mediæval spelling of ānulus a ring, dim of rare ānus a rounding, a circular form (see Lewis and Short).]
1. A ring, or ring-like body (in various technical applications).
1563. J. Shute, Archit., C j a. Thre of them ye shal geue to Echinus … the fourth part geue to Annulus.
1713. Derham, Phys. Theol., IV. xii. 223. These Rings have a Curious Apparatus of Muscles enabling those creatures … to dilate or contract their Annuli.
1761. Sterne, Tr. Shandy (1802), III. x. 275. By the return of the two ends of the strings thro’ the annulus or noose made by the second implication of them.
1794. Sullivan, View Nat., II. There is a prodigious annulus encompassing Saturn.
1853. Kane, Grinnell Exp., xix. (1856), 143. An annulus of Arctic shrubs and trees.
2. Geom. ‘The name of a ring, or solid formed by the revolution of a circle about a straight line exterior to its circumference as an axis, and in the plane of the said circle.’ Penny Cycl., 1834.
1802. Playfair, Illustr. Hutton. The., 508. If … the ring is a solid annulus … it may be so constituted that the attraction of Saturn … may produce a force perpendicular to its surface.
3. Bot. a. In ferns: The ring of cells that partially surrounds the sporangia. b. In mosses: The elastic external ring of epidermal cells with which the brim of the sporangium is furnished. c. In fungi: Sometimes applied to the portion of the veil, which remains like a collar round the stalk.
1830. Lindley, Nat. Syst. Bot., 313. The resemblance between the midrib of one of these scales and the annulus of a Polypodium.
1863. Berkeley, Brit. Mosses, 311. Annulus, a little ring, which is often elastic, at the rim of the mouth of the sporangium.
1871. M. Cooke, Fungi (1874), 19. The collar adherent to the stem falls back, and thenceforth is known as the annulus or ring.
4. Astr. A ring of light, as in an annular eclipse.
1871. trans. Schellen’s Spectr. Anal., § 54. 256. Forming an annulus around the Moon of about 8′ in diameter.
